This invention relates to the storage of grain in underground storage caverns, and more particularly, to apparatus and methods of storing grain in salt caverns and the loading and unloading of grain from the underground cavern.
The United States every year stores billions of bushels of surplus grain. The high stocks of grain are the result of low grain exports caused by the high prices for United States grains brought on by the Government's price support programs and a falling demand from grain importing countries as well as due to the normal requirement to store supplies from one season to the next. Because of the support program, the United States Department of Agriculture must locate storage space for the billions of bushels of grain. The United States faces a critical grain storage shortage, particularly in the corn belt, where most storage facilities are full. The country's estimated on-farm and commercial storage capacity is 23 billion bushels. However, much of the storage increase in recent years was in the form of temporary or non-traditional storage. Much of the emergency or temporary storage is to be replaced with more permanent storage.
There are two traditional types of grain storage facilities, the country elevator and the terminal facility. The country elevator is located close to the farmer and receives the farmer's initial shipments of grain at harvest. As the harvest season approaches, the country elevator will have stored grain moved to a terminal facility where it is stored for longer periods of time, pending sale to grain processors, users or export sales. Oftentimes the grain is stored in a terminal facility from three to five years. Physical storage times are generally short to prevent spoilage. Grain movement is normally by truck and rail.
Present grain storage facilities include silos and bins. The grain with high moisture content is dried in dryers prior to storage to remove excess moisture. This process reduces the danger of deterioration and permits the safe storage of the grain. The grain is oftentimes cleaned or aspirated to remove unwanted material as well as to improve the quality of the grain. Grain is sometimes mixed or blended with other grain in an effort to make a new lot which will be of an improved quality.
The Uniform Grain Storage Agreement with the U.S. Department of Agriculture's Commodity Credit Corporation requires that a federal license be issued by the U.S. Warehouse Act License Branch for any approved storage facility to insure that the facility meets required standards of the Commodity Credit Corporation. One of the federal license requirements includes the requirement that the facility be able to remove from storage, within thirty (30) working days, all of the grain for which the warehouse is or may be approved under the Uniform Grain Storage Agreement. However, it is not necessary that the removal capacity exceed 200 rail cars per day. In addition, there are moisture limits over which the Commodity Credit Corporation will not accept grain delivery. The Commodity Credit Corporation does not require that insurance be carried on Commodity Credit Corporation stored grain. Generally, the Commodity Credit Corporation utilizes grain storage filling the lowest cost facilities first and emptying them last. However, with the large grain surpluses and shortages in storage capacity, just about all of the storage space is being used at the present time.
In recent years, because of U.S. agricultural policies and because of the green revolution in Asia and now beginning in Africa, there has been a large year-to-year surplus of grain in the United States. This trend indicates that there is a growing need for grain storage capability, especially long-term storage. This continuing world surplus simply increases and lengthens the demand for storage and may ultimately require comparable storage in foreign countries.
Present grain storage facilities have used controlled atmospheres, especially nitrogen or carbon dioxide, for the storage of grain. High concentrations of these gases totally eliminate insects and virtually eliminate the growth of bacteria and fungi. Such controlled atmospheres also do not leave a chemical residue which can be of concern. These gases also eliminate any possibility of explosion or corrosion. One of the distinct disadvantages of present storage facilities is that such facilities are never truly air tight and require repeated applications of the nitrogen or carbon dioxide.
Experiments have shown that grain may be maintained in good condition for long periods of time while maintained in partial nitrogen atmospheres. With pure nitrogen and cooling, ten-year storage appears feasible, raising the possibility of national emergency grain storage in this and other countries. Results of tests have shown that grain with a 12.6% moisture content has virtually unchanged germination after 170 weeks. Grain has been found still fertile in air-tight Chinese tombs after 6,000 years.
Conventional storage structures have the disadvantage of providing a high surface to volume ratio of the grain thus allowing wide temperature fluctuations. Temperatures may rise to the point where the grain is destroyed. Thus, deterioration of grain is greatly retarded by lowering the storage temperature as well as the removal of oxygen.
It is known to store compressed air, gas, and liquid hydrocarbon products in subsurface storage caverns. Such storage caverns may be in salt, in hard rock, in depleted oil and gas reservoirs, in aquifers, and in mines. For example, strategic petroleum reserves are stored in underground salt caverns. Such salt caverns are developed in embedded formations or domes by conventional mining or by solution mining.
Oftentimes an underground salt cavern is developed for particular operating conditions and desired storage volume. The pre-designed salt cavern is formed using a leaching process conducted via wells which can extend to depths of several thousand feet depending upon the requirements and geological conditions. The leaching process includes drilling a borehole and setting casing into the salt formation, feeding fresh water through the casing to the cavern bottom and recovering the brine formed from the fresh water and salt through the inner annulus of the well casing. Indirect leaching feeds fresh water via the inner annulus into the upper region of the cavern and the brine in the lower region of the cavern is withdrawn via the flow bore of the casing string.
Products which have been stored or disposed in salt caverns include liquefied and gaseous hydrocarbons, compressed air, waste products in solid or liquified form, crude oil, LPG, NGL industrial and commercial gases such as ethylene, propylene, ethane, and refined oil products.
It is an object of the present invention to overcome the deficiencies of the prior art and utilize an underground storage facility which will store grain in a nitrogen or other controlled gaseous atmosphere. The present invention will further provide means for loading the underground storage cavern with grain and means for outloading the grain from the cavern through the well of the cavern.
Other objects and advantages of the invention will appear from the following description.